1. Technical Field
The present invention pertains to dispenser valves for liquid under pressure and has particular but not limited utility in dispensing effervescent liquids such as beer, soda pop, sparkling wine, etc.
2. Discussion of the Prior Art
A primary problem associated with dispensing effervescent liquids under pressure from a tap or spigot relates to the tendency of the liquid to foam or froth undesirably when forced under pressure through narrow openings of relatively short lengths or through sharp bends and turns. A short narrow opening typically causes the pressurized liquid to expand suddenly after passing the opening, resulting in turbulent foaming. Turbulence is also produced when the liquid is forced to flow around sharp bends before being dispensed.
This problem has been addressed in numerous patents, a typical example being U.S. Pat. No. 2,899,170 (Cornelius). This patent describes an independent decarbonation control device located upstream of an independently actuated faucet valve. The decarbonation control device includes a frusto-conical core member with an upstream portion tapering in an upstream direction to a rounded tip. This upstream portion of the core member is disposed in a similarly tapered frusto-conical chamber. For any given axial position of the core member in the chamber, the transverse annular spacing between the chamber wall and the core member remains constant throughout the core length. The resulting flow passage is thus a frusto-conical annulus of constant radial thickness and gradually increasing area as a function of downstream distance. The gradual increase in flow cross-sectional area over the length of the core member provides a gradual diffusion rather than a sudden expansion of the liquid flowing therethrough, and thereby prevents explosive turbulence and its undesirable foaming effects. Downstream of its frusto-conical portion, the chamber is cylindrical and contains a downstream portion of the core member which tapers slightly in a downstream direction to permit continued enlargement of the flow cross-sectional area. The axial portion of the core member in the chamber is adjusted by a screw to set the cross-sectional area for flow between the frusto-conical core and chamber portions. The goal is to set the axial position of the core member to achieve the desired flow rate for the effervescent liquid, and the position effectively depends on the driving pressure of the liquid and the pressure losses in the delivery line. When properly set the core member permits the effervescent liquid to be dispensed by the separately actuated faucet valve without excessive frothing while providing a reasonably fast flow rate under the existing conditions. It is known, however, that the driving pressure is sensitive to changes in ambient temperature and pressure. In addition, for some applications the driving pressure decreases as more liquid is dispensed from its container. Accordingly, in order to maximize the output flow rate as conditions change, it is necessary to repeatedly readjust the axial position of the core member in its chamber. Although this readjustment procedure is not of itself difficult, it is inconvenient and often ignored. The effectiveness of the core member as a decarbonation control device is therefore severely compromised in practice.
In British Patent Specification No. 1,486,245 (Leroy) there is disclosed a valve member that is movable along with the frusto-conical core member to permit both variation of the restrictor passage and opening/closing of the faucet with a single actuator. The valve member is located at the upstream end of the frusto-conical core member and comprises an annular shoulder on the core member positioned to mate with a similar shoulder on the annular valve seat at the inlet end of the chamber. An O-ring is placed on the core member shoulder to assure a pressure seal in the off position of the valve. Although this single actuator arrangement enhances the convenience of dispensing effervescent beverages, it does not minimize frothing. Specifically, the space between the shoulder region on the core member and the chamber wall immediately downstream of the seal is relatively large compared to the space of the valve opening between the O-ring and chamber wall as the valve is initially opened. The valve opening thus serves as a "pinch point" or restriction. Immediately downstream of this restriction, as the valve opens, the flow path for the effervescent liquid experiences a sudden expansion causing the liquid to virtually explode and froth as it passes beyond the valve pinch point. The frothing liquid then passes between the core member and chamber wall and is dispensed with an undesirably high foamy content.
In my U.S. Pat. No. 5,244,117 I disclose a single actuator dispenser valve wherein a frusto-conical core member has a rounded tip that seals the inlet opening at the narrow end of the frusto-conical valve chamber when the valve is closed. As the valve is opened, the rounded tip serves as a stagnation point to severely reduce the pressure of the liquid that is permitted to flow through the elongated and restrictive diffusing passage between the core member and the chamber wall. This arrangement reduces frothing as compared to the Leroy valve; however, even this arrangement is not optimal and can stand improvement.
I have also found that, in the valve of my aforesaid patent, cavitation tends to occur immediately downstream of the frusto-conical diffusion passage. Specifically, the gas in the flowing liquid tends to form bubbles which immediately collapse at this location within the valve. The result is a tendency to enhance undesirable frothing. Further, the volume of the valve chamber downstream of the core member has been found to be relatively important. Specifically, that volume must be small enough to maintain a sufficient back pressure to keep gas from escaping from the liquid within that volume.
I have also found that outlet spouts or spigots in prior valves for dispensing effervescent liquids are smoothly cylindrical along their internal surfaces. Liquid that drains through a spout from a larger volume naturally tends to flow vortically (i.e., eddy-like) rather than in a laminar straight fashion. The vortical flow results in turbulence and frothing in the egressing liquid.